Fix a crash when an Executor wrapped fork exit.

Fix rails#51298

Rails 7.0 was not wrapping `runner` command execution and Rails 7.2 changed the
definition of `active_connection?`. Therefore forking inside a script
intended to be run with the `runner` commmand crashes on 7.1.

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -194,7 +194,7 @@ def connection_class # :nodoc:
       # #connection or #with_connection methods. Connections obtained through
       # #checkout will not be detected by #active_connection?
       def active_connection?
-        @thread_cached_conns[connection_cache_key(current_thread)]
+        @thread_cached_conns.try(:[], connection_cache_key(current_thread))
       end
 
       # Signal that the thread is finished with the current connection.